Object tracking system with non-contact object detection and identification

ABSTRACT

An object tracking system is provided for tracking the removal of objects from a location and the replacement of the objects at the location. The system includes a radio frequency identification (RFID) tag attached to each of the objects to be tracked and each tag has an antenna. When activated, the RFID tag of an object transmits a unique code identifying the object. A storage unit is provided at the location and the storage unit has a plurality of receptacles configured to receive objects replaced at the location. Each receptacle has an associated antenna for activating the RFID tag of an object in the receptacle and receiving the radio frequency transmitted code of the object. The antennae of the system can be capacitive plates for conveying the radio frequency transmissions through capacitive coupling or inductive loops for conveying the transmissions through inductive coupling. A computer-based controller is coupled to the antenna of the receptacles for receiving transmitted codes and determining based thereon the absence or presence and location of objects within the storage unit.

REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the filing date of prior filedU.S. Provisional Patent Application serial no. 60/099,954, filed Sep.11, 1998.

TECHNICAL FIELD

This invention relates generally to object tracking and control systemsand more particularly to systems for tracking and controlling access toand disposition of objects such as keys.

BACKGROUND

Many objects have intrinsic value or have value because they provideaccess to other valuable objects. For instance, jewelry and coins haveinherent intrinsic value while keys, such as keys to vehicles, havevalue because they provide access to other valuable objects, namelyautomobiles and trucks. Further, access to and control of some items,such as narcotics for example, needs to be monitored, tracked, andcontrolled to assure against unauthorized access or assure that properand appropriate accesses catalogued. There is a serious need to be ableto track, catalogue access to, and control such objects in a way that isreliable, simple to implement, and virtually tamper proof.

In the past, a variety of systems have been implemented to track andcontrol objects. In the case of keys in an automobile dealership, forexample, pegboards have been used to keep track of the keys as salespersons, maintenance personnel, and others remove keys for access tovehicles. Generally, sign out sheets are used to log the check-in andcheckout of such keys. Obviously, such a manual system of tracking hasnumerous shortcomings due in large part to the very real potential ofhuman error and forgetfulness in carrying out the sign-in and sign-outprocedures.

More recently, automated computer controlled key tracking systems havebeen implemented for tracking, for example, vehicle keys at car lots andkeys to the apartments of apartment complexes. One such systemparticularly applicable to the present invention is the key trackingsystem disclosed and claimed in my U.S. Pat. No. 5,801,628 thedisclosure of which is hereby incorporated fully by reference. In thedisclosed system, referred to herein as the “Key Track” system, keys toa vehicle are attached with a rivet or the like to a thin plastic keytag or card having a depending tongue. The tongue carries a small buttonshaped electronic touch memory device, which electronically stores aunique code. The tongues of the key tags are configured to be insertablein an array of slots formed in a top panel within a storage drawer. Aprinted circuit backplane is disposed beneath the top panel and isprovided with a plurality of pairs of metal contacts, each pair ofcontacts being aligned with a corresponding one of the slots in the toppanel. When the tongue of a key card is inserted in a selected one ofthe slots, its touch memory device is engaged by the corresponding pairof contacts.

A computer or microprocessor or microcontroller based controller iselectronically coupled through a communications matrix to the contactson the backplane and periodically polls each pair of contacts,preferably several times per second, to determine the presence orabsence of a touch memory device and thus which slots contain key cardsand which do not. More specifically, if no information is received froma particular pair of contacts when polled, it is determined that theslot corresponding to the pair of contacts is empty. When a slotcontains a key card, the touch memory device of the card responds to thepoll by transmitting its unique code, from which the identity of theparticular key attached to the card can be determined through a tablelookup. In this way, the absence or presence and location in the storagedrawer of key cards and their associated keys can be noted by thecontroller each time the array of contacts are polled. If a card presentin a slot on a prior polling is absent on a subsequent polling, then thecontroller notes that the card and its key have been removed from thestorage drawer. Conversely, if a key card is detected in a previouslyempty slot, the controller notes that the card and its key have beenreplaced in the storage drawer. The removal and replacement of keys istherefore continuously monitored.

An access feature requires an authorized user such as a sales person toenter an ID code to unlock and access the storage drawer. When thehistory of removal and replacement of key cards and their keys iscombined with other information, such as the time at which cards areremoved and replaced and the identities of the persons who accessed thedrawer and times of access, access to the keys in the drawer can becontrolled and a detailed tracking log can be created. This Key Tracksystem greatly decreases instances of lost keys, reduces the timerequired to find checked-out keys, and generally provides automatictracking and control of the keys, and thus, to a large extent, controlsand tracks the vehicles to which the keys provide access.

While the Key Track system described above has proven extremely valuablein the tracking and control of keys, it nevertheless has certainproblems and shortcomings inherent in its design. For example, thebackplane of the system, which may contain dozens of upstanding metalcontacts for engaging the electronic touch memory devices of key cards,can be relatively complex and labor intensive to fabricate and requiresprecision in the placement and orientation of contact pairs. Inaddition, foreign items such as loose keys or other small metal itemsthat may inadvertently be dropped into or hang through one of the slotsin the top panel can and sometimes do short the contacts on thebackplane, resulting in the potential for false key tracking logs or, inextreme cases, error conditions that can result in degradation of theintegrity of the entire system. Furthermore, because the reading of thecodes stored in the touch memory devices relies upon physical contactbetween the touch memory devices and the electrical contacts on thebackplane, resistances that can result from corroded contacts or dirtytouch memory devices can also result in false and degrading readings.Additionally, the electrical contacts sometimes become bent or sprung sothat they fail to make proper contact with the touch memory devices ofkey cards placed in their corresponding slots. These and other relatedproblems all result from the requirement in the Key Track system thatobject detection and identification relies upon physical electricalcontact between a set of electrical contacts and an electronic touchmemory device.

Thus, even though the Key Track system has proven very useful andsuccessful, there exists a continuing need to enhance the system in sucha way that the problems mentioned above are addressed in an efficient,economic, and reliable way. It is to the provision of such enhancementsand improvements that the present invention is primarily directed.

SUMMARY OF THE INVENTION

Briefly described, the present invention, in one preferred embodimentthereof, comprises enhancements and improvements to the Key Track systemdisclosed in my U.S. Pat. No. 5,801,628 to address the problemsresulting from the requirement of physical electrical contact fordetecting and identifying objects. More specifically, the inventioncomprises an object tracking system for tracking the removal of objectsfrom a location and the replacement of the objects at the location. Inthe preferred embodiment, the objects to be tracked are thin plasticcards to which keys can be attached or small containers into which keysor other items can be placed. Keys may also be attached to the outsidesurfaces of the containers if desired. It should be understood, however,that the present invention is applicable to a wide variety of objectsother than these. The key cards and containers that are the “objects” inthe present disclosure are exemplary only and represent the best mode ofpracticing the invention, but are not intended to impose limitations onthe invention. In this disclosure, the term “objects” is used in thecontext of the preferred embodiment to refer to the key cards andcontainers in combination with the keys attached thereto. It should beunderstood, however, that the “object” should be interpreted to any itemthat is desired to be tracked and monitored with the system of thisinvention and is not limited to key cards, containers, keys, or anyother particular item.

An ID tag is attached to each of the objects to be tracked by the systemand each ID tag includes electronic storage means carrying a stored codeassociated with the object to which the ID tag is attached. If anotheritem, such as a key, is attached to the object, then the code alsoidentifies the other item. Each ID tag is adapted to transmit its storedcode by means of non-contact transmission such as, for example, radiofrequency transmission, when the ID tag is appropriately activated.

A storage unit is provided at the location with the storage unit havinga plurality of receptacles configured to receive objects when objectsare replaced at the location and to allow the objects to be selectivelyremoved from the storage unit when the objects are to be removed fromthe location. A sensor is associated with each of the receptacles in thestorage unit for activating the ID tag of an object in the receptacleand, in turn, detecting the resulting transmission by the ID tag of thestored code associated with the object. Selection circuitry is coupledto the sensors for successively selecting the sensors. Each sensor, whenselected, detects the stored code associated with an object if an objectis present in the corresponding receptacle and detects no code if anobject is not present in the corresponding receptacle.

A computer or microprocessor based or other appropriate controller iscoupled to the sensors through a communications link for receivingstored codes detected by the sensors and determining, based on thereceived codes, the absence of objects removed from the storage unit andthe presence and location within the storage unit of objects present inthe storage unit.

In the preferred embodiment, the ID tags attached to the objects areradio frequency identification (RFID) tags, which are adapted totransmit their stored codes through radio frequency transmission whenthe tags are appropriately activated. Each of the ID tags includes anantenna for transmitting its stored code and, in one embodiment, forreceiving data to be stored or acted on by the RFID tag. Each of thesensors includes an antenna for activating the RFID tags and receivingstored codes transmitted thereby and/or convey data to the RFID tags. Inone preferred embodiment, the antenna of each RFID tag comprises a pairof capacitive plates located on the object and the antenna of eachsensor comprises a pair of capacitive plates positioned to align withthe capacitive plates of an RFID tag when an object bearing the RFID tagis placed in the corresponding receptacle of the storage unit. Inanother embodiment, the antenna of each RFID tag comprises an inductiveloop antenna coupled to the RFID tag and the antenna of each sensorincludes a corresponding inductive loop positioned to align with theloop of an RFID tag when an object bearing the RFID tag is inserted in acorresponding receptacle of the storage unit. In either case, the RFIDtag of an object in a receptacle of the storage unit is activated whenradio frequency power is supplied to the antenna of the sensorcorresponding to the receptacle and the code of the RFID tag is detectedby the sensor and conveyed through the communications link to thecontroller. Thus, detection and identification of objects within thestorage unit is accomplished through non-contact radio frequencytransmissions.

The object tracking system of the present invention provides a number ofadvantages over systems requiring physical electrical contact fordetection and identification of objects in a storage unit. For example,since codes are conveyed not through physical contact but rather throughradio frequency transmission or through modulation of a radio frequencysignal, foreign objects that may fall into the storage unit do notresult in shorted contacts and have little effect on the integrity andreliability of the system. Further, when this invention is applied to anobject tracking system including a panel with receptacles and abackplane, the antenna of the sensors can be formed on the backplane ininexpensive and reliable ways such as, for example, through commonprinted circuit board etching techniques. The sensors can be formed onthe back side of the backplane if desired to protect the sensorsfurther. Thus, not only is the system more reliable than prior artsystems, it is also more economical to produce. Finally, because thedetection of codes is accomplished through radio frequencytransmissions, problems associated with interference or cross-talk inthe data matrix that must be addressed with systems employing physicalcontacts are much less prevalent and, even where present, are simpler toaddress. Also, since no physical electrical contact is required fordetecting codes, problems associated with corroded or bent contacts ordirty touch memory devices are eliminated altogether. As a matter offact, the present object tracking system functions as well in commonlyencountered dirty or corrosive conditions as in clean conditions.Finally, since the RFID tags have no polarity requirements as dophysical contacts, the objects can be placed in the slots in anyorientation.

Thus it is seen that an improved object tracking system is now providedthat successfully addresses the shortcomings of prior systems whereinphysical electrical contact has been required for object detection andidentification. The system lends itself to a wide variety ofapplications where it would otherwise be difficult to employ systemsrequiring physical electrical contacts and is economical, robust, andreliable. These and other features, objects, and advantages will becomemore apparent upon review of the detailed description set forth belowwhen taken in conjunction with the accompanying drawings, which arebriefly described as follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an object in the form of a key card foruse with an object tracking system of this invention illustrating onepreferred placement and configuration of a capacitive plate antenna andRFID tag.

FIG. 2 is a perspective view of an object in the form of a key cardillustrating an alternate configuration of the capacitive plate antenna.

FIG. 3 is a perspective view of an object in the form of a box orcontainer bearing an RFID tag with a capacitive plate antenna having apreferred configuration.

FIG. 4 is a perspective view of the container of FIG. 3 opened to revealits interior and placement of the RFID tag and its capacitive plateantenna.

FIG. 5 is a functional block diagram of an object tracking system thatembodies principles of the present invention in a preferred form.

FIG. 6 is a functional block diagram showing the components of an RFIDtag attached to an object to be tracked.

FIG. 7 is an exploded perspective view illustrating a preferredimplementation of the object tracking system of this invention whereinthe sensors of the system are formed on a backplane positioned beneath areceptacle panel of a storage unit.

FIG. 8 is a top plan view illustrating alignment of the capacitive plateantenna of an RFID tag on an object with the capacitive plate antenna ofa sensor on the backplane of FIG. 7.

FIG. 9 is a simple functional schematic illustrating interrelations ofthe components of the present invention.

FIG. 10 is an electronic schematic illustrating one preferred mode ofimplementing principles of the present invention.

FIG. 11 illustrates one configuration of the capacitive plate sensors onthe backplane of the system.

FIG. 12 illustrates an alternate configuration of the capacitive platesensors on the backplane.

FIG. 13 illustrates an alternate embodiment of the present inventionwherein the antennae of the ID tags and the antennae of the sensors areinductive loops.

FIG. 14 is a perspective view illustrating an alternate configuration ofthe inductive loop antenna embodiment of this invention.

FIG. 15 is a perspective view showing yet another configuration of theinductive loop antenna embodiment of the invention.

FIG. 16 is an electronic schematic diagram showing a preferredimplementation of the inductive loop antenna embodiment on the backplaneof a storage unit.

FIG. 17 is a cross-sectional view of a portion of a storage unit showingthe inductive loop antenna embodiment of FIG. 16.

FIG. 18 is a perspective view illustrating an alternate application ofthe present invention for tracking file folders within a filing cabinet.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described in detail within the generalcontext of a key or small item tracking system. In such a system, keysto vehicles are attached to key cards (or placed in or on the outsidesurface of small containers), which are checked out from and replaced ina centrally located storage unit. Each key card is provided with an RFIDtag. The storage unit preferably has a top panel formed with an array ofreceptacles for receiving the key cards. A backplane is disposed beneaththe panel and has an array of sensors for detecting and identifying keycards located in the receptacles of the storage unit. This configurationis discussed in detail in my issued patent, which provides backgroundfor the discussions that follow.

Even though a preferred embodiment of the invention is as a key or smallitem tracking system, it should be kept in mind during review of thedetailed description that follows that the invention has a wide varietyof uses wherever there is a need to track access to and location ofobjects. In many such configurations, the RFID tags may be attacheddirectly to the objects that ultimately are to be tracked, although inthe preferred embodiments, the “objects” to which the RFID tags areattached are key cards or containers and the keys attached thereto arethe items ultimately to be tracked. The particular context within whichthe invention is described should therefore not be considered to be alimitation of the invention.

Referring now in more detail to the drawings, in which like numeralsrefer to like parts throughout the several views, FIG. 1 illustrates akey card for use with a Key Track system embodying principles of thepresent invention. The key card 11 is generally rectangular in shape andhas a top edge 12, a bottom edge 13, a right side edge 14, and a leftside edge 16. The card 11 defines a front face 17 and a rear face 18(not shown in FIG. 1) and is sized to be inserted in and removed fromany of a number of slots or receptacles in a storage unit. An attachmentlug 24, which may be a rivet or some other attachment mechanism, ismounted adjacent top edge 12 of the card for attaching a key or a set ofkeys to the card. A radio frequency identification (RFID) tag 19 isattached to the card 11 adjacent its bottom edge 13. The RFID tag 19includes an integrated circuit chip 21 coupled to an antenna, which, inthis embodiment, comprises a capacitive plate antenna defined by firstcapacitive plate 22 and a second capacitive plate 23. The capacitiveplates 22 and 23 can be fabricated of any suitable conductive orsemiconductive material such as, for example, conductive foil or, morepreferably, resistive ink.

RFID tags such as those illustrated in FIG. 1 and throughout the figuresof this disclosure are commercially available devices and can beobtained from a number of suppliers including Microchip Corporation,Motorola, and Texas Instruments. At this writing, only Motorola is knownto supply capacitive RFID tags while all of these companies supplyinductive loop RFID tags. Also available from these suppliers are the“chip sets” that accompany the RFID tags. These chip sets includerelated electronic components such as encoder/decoder chips fordetecting and decoding information conveyed by the RFID tags. Ingeneral, two types of RFID tags are available; inductive tags andcapacitive tags. Application of inductive RFID tags in the presentinvention is described below. Capacitive RFID tags, one of which isavailable from Motorola under the trade name Bistatix, are suitable foruse in the present invention. In general, the distinction betweeninductive and capacitive RFID tags is that in inductive tags, radiofrequency information is conveyed through inductively coupled loopantennas and in capacitive tags, radio frequency information is conveyedthrough capacitively coupled plate antennas. The detailed operation ofRFID tags is beyond the scope of the present disclosure. Such detailinformation is published by the manufacturers of these devices and isgenerally available.

FIG. 2 depicts an embodiment of a key card that embodies principals ofthe invention in an alternate form. The key card 26 is similar to thekey card 11 of FIG. 1 and has a top edge 27, a bottom edge 28, a rightside edge 29, and a left side edge 31. The card defines a front face 32and a back face 33 (not visible in FIG. 2). An RFID tag 34 is attachedto the card 26 adjacent its bottom edge. The RFID tag 34 comprises anintegrated circuit chip 36 and an associated antenna formed by a firstcapacitive plate 37 and a second capacitive plate 38. The alternateembodiment of FIG. 2 is similar in all respects to the embodiment ofFIG. 1 except that, in FIG. 1, the capacitive plate antenna is arrayedhorizontally adjacent the bottom edge 13 of the card while in FIG. 2 thecapacitive plate antenna is arrayed vertically. The implications andapplications of these alternate configurations are discussed in moredetail below.

In FIGS. 1 and 2, the RFID tags, including their antennae, areillustrated as being attached to the front faces of their respective keycards. It will be understood, however, that the tags and their antennaecan just as well be attached to the back faces of the cards, covered bya protective coating, or, even more preferably, embedded within thematerial of the cards themselves. Embedding the RFID tags and theirantennae is advantageous since they are then protected from the elementsand from being scratched or scraped off of the card as a result of roughhandling.

FIG. 3 illustrates yet another alternate and preferred embodimentcomprising an openable container 41 for use with an object trackingsystem of this invention. The container 41, which may be molded ofplastic, comprises a top side 42, a bottom side 43, a right side 44, anda left side 46. A back panel 47 closes the back of the container and ahingeable cover 47, when shut, closes the front of the container todefine an interior compartment within the container. An attachment lug57 can be provided within the compartment or, alternatively, on theoutside of the container if preferred for attaching keys or otherobjects to the container. A capacitive RFID tag is attached to thebottom side 43 of the container 41, preferably on the inside of thecontainer. As with the embodiments of FIGS. 1 and 2, the RFID tag 52comprises an integrated circuit chip 53 and an associated antenna formedof a first capacitive plate 54 and a second capacitive plate 56.

FIG. 4 illustrates the container 41 of FIG. 3 in its open configuration.The attachment of the RFID tag 52 to the inside surface of the bottomside 43 of the container is illustrated more clearly. Attaching the RFIDtag in this manner provides for ease of fabrication techniques. In fact,one configuration in which capacitive RFID tags may be available is inthe form of adhesive stamps or stickers, which can simply be adhered tothe interior surface of the bottom side 43 of the container during thefabrication process. Alternatively the RFID tag can be attached to theoutside surface of the bottom side or embedded within the plasticmaterial of the container to protect it from contamination and abuse.

While the embodiment of FIGS. 3 and 4 is illustrated as a container withan interior compartment for containing keys or other objects, it mayjudiciously be fabricated as a permanently or semi-permanently closedstructure with an attachment lug on the outside. In such aconfiguration, the embodiment of FIG. 3 would function similar to a keycard such as those shown in FIGS. 1 and 2 but the RFID tag would belocated on the bottom of the closed container and would be enclosed toprotect it from the elements and to provide more efficientimplementation in a system having a storage unit with a top paneldefining compartments and a backplane, as described in more detailbelow.

FIG. 5 illustrates, in the form of a functional block diagram theprimary elements of an object tracking system making use of RFID tagssuch as those illustrated in FIGS. 1-3. In many respects, this system issimilar to that disclosed in U.S. Pat. No. 5,801,628. In general, thesystem comprises a number of objects to be tracked, one such object 61being illustrated in FIG. 5. These objects can be key cards orcontainers as shown in FIGS. 1-3 or virtually any other type of objectwhose removal and replacement at a central or storage location needs tobe tracked. An RFID tag 62 is attached to each object 61. As with priorKey Track systems, the goal of the object tracking system of thisinvention is to determine the absence or presence and location ofobjects at a central location wherein a storage unit having a number ofRF sensors 63 may be present. As described in more detail below, each ofthe RF sensors at the location is associated with an object receptacleand is electronically coupled to a matrix selector, which has theability to activate or, in other words, to apply an RF carrier signal tothe RF sensors sequentially or otherwise. Activation of an RF sensor 63associated with a receptacle where an object 61 is present causes theRFID tag 62 of the object 61 to activate and convey its storedidentification code to the RF sensor 63. The codes conveyed by the RFIDtags to the RF sensors are received and decoded by a radio frequencyencoder/decoder 66. The matrix selector and RF encode/decoder areconnected to a computer or microprocessor based controller 67, whichdirects the activities of these devices to track and log the removal andreplacement of objects 61 at the location.

FIG. 6 illustrates, in the form of a functional block diagram, the majorcomponents of a typical RFID tag. As mentioned above, such tags arecommercially available and their detailed operation is beyond the scopeof this disclosure. However, a general understanding of their operationis helpful. Further, while FIG. 6 illustrates a passive RFID tag, itwill be understood by those of skill in the art that active RFID tagsare also available and can be used. Active tags generally include theirown power source and some are capable of receiving and storinginformation as well as conveying information as do passive RFID tags. Inthe passive RFID tag 71 illustrated in FIG. 6, a parasitic power system72 is provided on the chip for drawing electrical power from the radiofrequency signal produced by the antenna of an adjacent RF sensor. Anelectronic memory 74 is provided for storing the unique code of the RFIDtag and an encoder/decoder 73 is coupled to the memory for producingradio frequency modulations that carry the unique code stored in memory.The encoder/decoder and power system are coupled to an antenna 76, whichcan be a capacitive plate antenna such as that illustrated in FIGS. 1-4,an inductive loop antenna, or another appropriate type of antenna. Theantenna of the tag is adapted for radio frequency coupling to theantenna of an RF sensor to convey the code of the RFID tag to the sensorand on to the controller of an object tracking system for processing.

FIG. 7 depicts one preferred embodiment of an object tracking systemthat embodies principles of the invention in a preferred form. In thissystem the objects to be tracked comprise the containers 41 (and theirattached keys) illustrated in FIG. 3 with the containers having RFIDtags 52 with an antenna formed by capacitive plates 54 and 56. It shouldbe understood that principles illustrated in FIG. 7 are equallyapplicable to other objects to be tracked and to other configurations ofRFID tags.

The system of FIG. 7 comprises a storage unit such as, for example, adrawer, generally indicated at 81, at a location where the objects 41are to be checked out and checked back in by personnel. The storage unit81 includes a top panel 82 formed with an array of openings 83, each ofwhich define a receptacle sized and configured to receive an object 41.Since the RFID tags are polarity insensitive, the slots need not bekeyed to ensure a particular orientation of the object 41 when insertedin a receptacle. The storage unit 81 also includes a backplane 84, whichis disposed beneath and spaced from the top panel 82. The backplane 84,which preferably takes the form of a printed circuit board, carries theradio frequency sensors and related electronics for receiving the codesof RFID tags attached to objects inserted in the receptacles 83. Morespecifically, an RF sensor corresponding to and aligned with each of thereceptacles 83 is formed on the backplane and comprises a capacitiveplate antenna formed by a first capacitive plate 87 and a secondcapacitive plate 88.

The capacitive plates 87 and 88 are positioned on the backplane 84 suchthat they align with the capacitive plates 54 and 56 attached to anobject inserted in the corresponding receptacle 83. That is, when theobject is inserted in the receptacle such that its bottom side rests onthe backplane, the capacitive plates 54 and 56 attached to the objectalign with and are disposed adjacent to the capacitive plates 87 and 88of the respective sensor. While the capacitive plates 87 and 88 areshown on the top surface of the backplane in FIG. 7, they can also beformed on the bottom surface if desired to provide better protection.

One of the capacitive plates 88 of each RF sensor is connected to radiofrequency ground 94 while the other is coupled, through a radiofrequency switch 89, to a radio frequency source 93. Each radiofrequency switch 89, in turn, is connected to a row and column selectionbuss and all the row and column selection busses are electronicallycoupled to the matrix selector. The matrix selector is configured toaddress the row and column of an RF sensor in the array of sensors toactivate that sensor for receiving codes of an object, if any, in thereceptacle corresponding to the sensor. By “selection” it is meant thata radio frequency carrier signal is applied to the plates of the sensorthrough the switch 89. One implementation of this selection or switchingor polling process is described in more detail below.

The storage unit 81 is indicated generically in FIG. 7. It should beunderstood that this unit can take on a number of different variationsand configurations. For example, the panel 82 and backplane 84 can bedisposed in a lockable drawer such as that illustrated in U.S. Pat. No.5,801,628. Alternatively, the system could be configured as a verticallyoriented wall panel or in any other form convenient for storing theparticular objects desired to be tracked. Accordingly, the particularconfiguration of the storage unit in the context of which thisapplication is described should not be considered to be a limitation ofthe invention, even though it is considered by the inventor to be a bestmode of practicing the invention.

The object tracking system shown in FIG. 7 is similar in some functionalrespects to that of prior Key Track systems. Specifically, the matrixselector, controlled by the controller, sequentially activates or pollsthe RF sensors on the backplane. If an object 41 bearing an RFID tag 52is present in a receptacle corresponding to a particular RF sensor, theRFID tag of the object is activated upon selection of the sensor toconvey its code to the RF sensor. The code is then transmitted orconveyed to the controller, which notes that the object corresponding tothe received code is present in the storage unit and is located in thereceptacle corresponding to the RF sensor that received the code.Alternatively, if no code is received when a sensor is polled, thecontroller notes that there is no object present in the receptaclecorresponding to that sensor.

By sequentially polling the sensors in relatively rapid order(preferably several times per second) the controller is able to log whenobjects are removed from the storage unit, when they are replaced, andalso the location or receptacle within the storage unit where an objectis located. More specifically, if an object is detected in a receptacleduring one polling cycle and is not detected in a subsequent cycle, thenthe controller notes that the object has been removed from the storageunit. Alternatively, if no object is noted on a polling cycle and anobject is detected on a subsequent polling cycle, then the controllernotes that the object has been replaced in the storage unit and that itis located at the receptacle corresponding to the sensor that detectedthe object. As with prior Key Track systems, this information can becompiled to create logs, reports, control commands, alarm generatingsignals, and otherwise for tracking and controlling access to theobjects.

FIG. 8 illustrates the alignment of the capacitive plate antennaattached to an object with the capacitive plates of an RF sensor on thebackplane of the system of FIG. 7 when the object is placed in areceptacle corresponding to the RF sensor. Specifically, the capacitiveplates 54 and 56 of the RFID tag attached to the object 41 each alignwith a respective one of the capacitive plates 87 and 88 and aredisposed closely adjacent to but generally not contacting the sensorplates (although the system will operate with the plates in contact. Inthis way, a parallel plate capacitor is formed by each capacitive plateof the RFID tag and the corresponding capacitive plate of the RF sensoron the backplane. As mentioned above, one of the capacitive plates ofthe RF sensor is coupled to radio frequency ground at 80 while the otheris coupled to a radio frequency source 93 through a radio frequencyswitch 89. The switch can be activated when the row and column of theswitch is selected by the matrix selector through a row select line 91and a column select line 92. When the row and column of the sensor isnot selected, the radio frequency switch is off, the RF carrier signalis not applied to plate 87, and the RF sensor at that location is notactivated.

FIG. 9 is a functional electronic schematic diagram illustrating theinteractions of the various components of the system. On the right, theRFID tag, which in reality is all incorporated on the integrated circuitchip 53 (FIG. 8), includes its parasitic power circuit, encoder/decoderand modulator circuit, and memory. The antenna comprising, in thisembodiment, capacitive plates 54 and 56, is coupled to the RFID tag andshown adjacent to the RF sensor's antenna comprising capacitive plates87 and 88. Capacitive plates 54 and 87 form a parallel plate capacitorand plates 56 and 88 also form a parallel plate capacitor. Capacitiveplate 87 of the sensor is selectively couplable through radio frequencyswitch 89 to the radio frequency source 106 and encoder/decoder 66. Apractical RF source 106 has series source resistance 108 and a sourcereactance 107. The encoder/decoder 66 is connected across the combinedsource module 106, 107, and 108. The encoder/decoder 66 and the matrixselector 64 are controlled by the controller 67.

In general, the circuit of FIG. 9 operates as follows. When it isdesired to poll the RF sensor to determine if an object is present inits associated receptacle, the controller triggers the matrix selector64 to close the radio frequency switch 89 corresponding to the sensor.This couples capacitive plate 87 of the sensor's antenna to the radiofrequency source 106. The radio frequency signal produced by the radiofrequency source 106, in turn, is coupled by means of capacitivecoupling to the capacitive plate 54 of the RFID tag. In thisconfiguration, the capacitors essentially function or appear as short orvery low impedance circuits to the RF signal, thus essentiallyconnecting the RF signal directly to the RFID tag. The parasitic powercircuit 72 within the RFID tag draws power from the radio frequencysignal and, when sufficient power has been stored, theencoder/decoder-modulator circuit 73 is activated. The encoder/decodermodulator 73 then accesses the memory 74 and generates a modulating loadacross the capacitive plates 54 and 56 with the modulationscorresponding to the unique code retrieved from memory. This processgenerally is known as “keying” and information can be modulated onto anRF carrier wave through various types of keying such as, for example,frequency shift keying (FSK), phase shift keying (PSK), or amplitudeshift keying (ASK), and/or amplitude modulation. A discussion of suchkeying techniques is beyond the scope of the present disclosure, but allare known and understood by those skill in the art. The modulating loadcreated by the encoder/decoder-modulator, in turn, causes thecharacteristics of the radio signal measured across the source 106, 107,and 108 to modulate in proportion to the modulations generated by theRFID tag. The encoder/decoder 66 is adapted to monitor these modulationsand decode them into the original code stored in the memory 74 of theRFID tag. In this way, the RFID tag conveys its unique code to theencoder/decoder, which transmits it onto the controller for analysis.The controller can then determine the identity of the object bearing theRFID tag and process the information in an appropriate way.

While not illustrated in FIG. 9, an active RFID tag could also be used.As mentioned above, such active tags are able to receive and storeinformation as well as transmit information. In such a system, theencoder/decoder 66 would also modulate the radio frequency signalsupplied to the sensor. The encoder/decoder 73 of the RFID tag wouldthen decode these modulations, extract the information containedtherein, and store the information in a storage memory. Such a systemcould have a wide variety of uses. For example, the identity of theperson checking out the object or other useful information might bestored in the RFID tag for access and processing at a later time. Bothpassive and active RFID tags are considered to be within the scope ofthe present invention.

FIG. 10 is a detailed electronic schematic diagram illustrating onepossible circuit implementation of the present invention. It will beunderstood by those of skill in the art that various other electroniccircuits might also be applied to accomplish the same result; however,the circuit of FIG. 10 is preferred because of its simplicity andreliability.

In FIG. 10, the radio frequency source comprising elements 106, 107, and108 is selectively couplable to the active plate 87 of each sensor ateach location in the storage unit. While six such sensors areillustrated in FIG. 10 for clarity, it will be understood that an actualimplementation might include dozens or more sensors. Selection andactivation of a sensor will be described herein with reference to thesensor at location I on FIG. 10; however, the same discussion applies tothe other sensor locations J, K, L, M, and N. When it desired toactivate or select the sensor at location I, the controller, through thematrix selector, sets the row select 109 for row 1 to a low state andthe column select 92 for column 1 to a high state. The low state of therow select 109 causes the N-channel MOSFET inverting switch 112 to setthe row trace 113 to a high state. Similarly, the high state of columnselect 92 turns on transistor 121, pulling the column trace 114 to a lowstate. This causes diode 119 to be forward biased, which turns the diodeon and connects capacitive plate 87 of the sensor at location I to theradio frequency source 106. Thus, the sensor at location I is activated,i.e. is connected to the RF carrier signal. However, the sensors at theother locations are not activated because their diodes are maintained ina reverse biased condition since only transistor 121 at column 1 isturned on.

Capacitor 118 forms a high pass filter that blocks DC voltages of theselection matrix from being transferred back to the RF source whileallowing radio frequency modulations from an RFID tag to be transferredback for interpretation by the RF encoder/decoder 66. Inductances 117and 124 form RF chokes that isolate row and column selector circuitryfrom the RF signals. If an object bearing an RFID tag is present atlocation I, its code will be conveyed to the RF encoder/decoder and thentransmitted to the controller 64 in the manner previously described. Ifno object is present at location I, no code will be received. Thecontroller can thus determine the absence of an object at location I orthe presence of an object at location I.

The process is repeated sequentially for sensors at locations J, K, etc.by activating the appropriate row and column trace to forward bias theirdiode switches and connect them to the radio frequency source 106 andthe encoder/decoder 66. Preferably, as mentioned above, the sensors atthe various locations are polled continuously at a relatively high rateof several times per second. In this way, the controller can easilydetermine the time at which objects bearing RFID tags are removed andreplaced at the storage location.

FIG. 11 illustrates an embodiment of the backplane of the presentinvention wherein the key card 11 of FIG. 1 is used. A receptacle 131 inthe top panel of a storage unit (shown in phantom line in FIG. 11 forclarity) is sized to receive a key card 11. A backplane 132 is disposedbeneath the top panel and spaced therefrom. Preferably, the backplane132 also has a slot 133, which receives the bottom edge 13 of the keycard 11 for aligning the key card within the storage unit. Capacitiveplates 134 and 141 form the sensor in this embodiment. Capacitive plate134 is configured with an upstanding leg 136 and an attachment tab 137.The attachment tab 137 is attached to the backplane 132 by means ofrivets 138, or other appropriate fasteners. Similarly, capacitive plate141 has an upstanding leg 142 and an attachment tab 143 attached to thebackplane 132 by means of rivets 144. Capacitive plates 134 and 141 areattrached to the selector circuitry and RF source as previouslydescribed.

With this configuration, it will be seen that when the key card 111 isinserted into the receptacle 131, the capacitive plates 22 and 23 of itsRFID tag 19 align with capacitive plates 134 and 141 of the sensor.Activation of the RFID tag and conveyance of its code can thus beaccomplished as described above.

FIG. 12 illustrates an embodiment of the object tracking system for usewith the key card 26 illustrated in FIG. 2. Here, the capacitive plates37 and 38 of the RFID tag's antenna are oriented vertically on the keycard 26. A receptacle 146 in a top panel is sized to receive the cardand an alignment slot may also be provided in the backplane 147 ifdesired. A daughter board 148 is attached to and projects upwardly fromthe backplane 147. The daughter board 148 carries the sensor's antenna,which can be formed through PC board etching techniques and whichcomprises capacitive plates 149 and 151. Capacitive plate 149 iselectrically connected to other components of the system such as theselector circuitry and RF source through a trace 150 and capacitiveplate 151 is similarly connected through a trace 152. Preferably, thedaughter board 148 is a small printed circuit board and the capacitiveplates 149 and 151 are formed through standard printed circuit etchingtechniques, although other techniques can be used. When the key card 26is inserted in the receptacle 146, its capacitive plates 37 and 38aligned with capacitive plates 149 and 151 respectfully for activationof the RFID tag and transfer of its code to the controller.

FIG. 13 illustrates an alternate embodiment of the object trackingsystem of this invention, which makes use of inductive RFID tags ratherthan capacitive tags. Here, key card 156 has a top edge 157, a bottomedge 158, a right side edge 159, and a left side edge 161. The carddefines a front face 162 and a back face 163 (not shown). An attachmentlug 164 is provided for attaching a key or other item to a card. An RFIDtag 166 is attached or embedded within to the key card and comprises aintegrated circuit chip 167 and an antenna 168, which, in thisembodiment, takes the form of a loop antenna 169.

The card 156 bearing RFID tag 166 is inserted in a receptacle 170 formedin the top panel of a storage unit. The unit's backplane 171 is providedwith an upstanding daughter board 172 corresponding to the receptacle170. The daughter board 172 carries the antenna of the RF sensor in theform of a looped antenna 173 that is connected to other components ofthe system through traces 174. When the key card 156 is inserted in thereceptacle 170, its inductive loop antenna 168 aligns with the loopantenna 173 on the daughter board 172. Radio frequency energy can thenbe transferred to and from the RFID tag in the same way as with thecapacitive RFID tag described above. However, in this embodiment, theradio frequency energy and information carried by modulations thereof isconveyed through inductive coupling between the two loop antennas 168and 173. Otherwise, the system functions in the same way as the previouscapacitively coupled embodiment.

FIGS. 14 and 15 illustrate yet further embodiments of the system of thisinvention wherein inductive radio frequency coupling is used to detectand identify objects. In FIG. 14, the object 181 is a key tab having anattachment card 182 and an attachment lug 183 for attaching a key orother object to the card. A stem 184 depends from the attachment card182 and has an interior bore 186 forming a socket in the depending stem184. An RFID tag is attached to or embedded in the object and includesan integrated circuit chip 188 and inductive loop antenna 187 coupledthereto. The inductive loop antenna extends around the stem 184 in aspiral wrapped fashion surrounding the socket 186.

The stem 184 of the object 181 is inserted through an opening 189 in atop panel to replace the object in a storage unit. A backplane 191 isprovided with a sensor post 192, which projects upwardly from thebackplane 191 and is aligned with the receptacle 189. The sensor post192 is provided with a sensor in the form of an inductive loop antenna193 that wraps around the post and that is connected to other componentsof the system through traces 194. When the object 181 is insertedthrough the receptacle 189, the sensor post 192 is received in thesocket 186 in such a way that the inductive loop antenna 193 of thesensor is disposed within and concentric with the inductive loop antenna187 of the RFID tag. Communication between the system and the RFID tagis then possible as previously described. One advantage of theembodiment of FIG. 14 is that radio frequency electromagnetic fields canbe concentrated by the multi turn concentrically disposed inductive loopantennas, making for more efficient coupling of RF signals.

FIG. 15 illustrates yet another embodiment of the same concept. Here, anobject to be tracked has a depending stem 196 bearing an RFID tag havingan integrated circuit 198 and an inductive loop antenna 197. Thebackplane of the system is provided with an inductive loop antenna unit199 having a central opening 102. When the stem 196 of the object isinserted into a receptacle corresponding to a position in the storageunit, it is received through the opening 102 in the loop unit 199.Communication with the RFID tag then takes place as previouslydescribed.

Another configuration of the inductively coupled object tracking systemis shown in FIGS. 16 and 17. FIG. 16 illustrates the backplane of astorage unit with its various electronic components and with inductiveloop antennas formed on the backplane by printed circuit board etchingtechniques. Specifically, each sensor location on the backplane has acorresponding inductive loop antenna trace 206 extending around acentral opening 207 for receiving the stem of a object placed in thestorage unit. With reference to FIG. 17, the stem 216 of such a unit isinserted through a receptacle 222 in a top panel 221 until its stemextends through the corresponding opening 207 in the backplane 205. Thestem 216 is provided with an RFID tag comprising an integrated circuitchip 218 and an inductive loop antenna 217. When in position, theinductive loop antenna 217, having multiple turn inductive loops 219, isdisposed in the center of the inductive loop traces 224 on the backplane205. Preferably, inductive loop traces 224 are formed both on the topand bottom surface of the backplane to increase the radio frequencyfield strength. Communication with the RFID tag then takes place throughinductive coupling as described above.

FIG. 18 illustrates an alternate application of the object trackingsystem of the present invention. In this application, the storage unitcomprises a filing cabinet 226 having a case 227 and a plurality ofdrawers 228. The drawers are configured to carry file folders 229 in theusual way. Each of the file folders is provided with an RFID tag 231,which, in the illustrated embodiment, is an inductive RFID tag. Aninductive loop antenna 232 is provided on the back of the drawer 228 andis connected through flexible cabling 233 to the controller 234, whichcontains the other electronic components described above. The otherdrawers of the filing cabinet 226 also are provided with antennae thatare coupled to the controller 234 by means of a buss 236.

In use, the controller 234 sequentially polls the antennae 232 in thedrawers of the filing cabinet (or in several filing cabinets ifdesired). When the antenna of each drawer is activated, the RFID tags offile folders 229 within the drawer are activated and transmit theirunique codes to the antenna 232. The controller 234 then detects thesecodes and can determine from the codes received, which files are in thedrawer. In addition, when polled rapidly such as, for example, severaltimes per second, the controller can determine when files are removedfrom drawers, when they are replaced, and which drawer they are in whenreplaced. This information can be used in a variety of beneficial ways,including the elimination of structured filing systems, which can becumbersome to maintain. With the object tracking system of the presentinvention applied to a filing cabinet, a user need only ask thecontroller where a file is located and the controller can indicatedwhich drawer of which cabinet contains the file. If the file has beenchecked out by another individual, the controller can inform the userthe identity of the person who has the file. These and other advantagesof the application applied to a filing system are possible.

The invention has been described herein in terms of preferredembodiments and methodologies. More specifically, the invention hasprimarily been described in terms of a system for tracking keys or othersmall objects that can be attached to a key card or enclosed in acontainer. While these are preferred applications of the invention, itwill be understood that the invention is fair from limited to thespecific embodiments and applications discussed herein. Virtually anytypes of objects that need to be tracked can be tracked with the presentinvention as long as they can be provided with RFID tags and a storagereceptacle for receiving the objects. Thus, a wide variety of additions,deletions, and modifications might well be made to the embodimentsillustrated herein without departing from the spirit and scope of theinvention as set forth in the claims.

What is claimed is:
 1. An object tracking system for tracking theremoval of objects from a storage unit and the replacement of theobjects at a storage unit, said object tracking system comprising: apanel disposed in said storage unit, said panel being formed withopenings defining a plurality of receptacles for receiving objects to betracked; a backplane in said storage unit; an ID tag attached to each ofthe objects to be tracked, each ID tag including electronic storagemeans carrying a stored code associated with the object corresponding tothe ID tag, each of said ID tags transmitting its stored code when saidID tag is appropriately activated; said plurality of receptacles in saidpanel being configured to receive objects when objects are replaced insaid storage unit and to allow the objects to be selectively removedfrom the storage unit; a sensor associated with each of said receptaclesfor activating the ID tag of an object in said receptacle and detectingthe resulting transmission by the ID tag of the stored code associatedwith the object, said sensors being supported on said backplane;selection circuitry coupled to said sensors for successively selectingsaid sensors, each sensor, when selected, detecting the stored codeassociated with an object if an object is present in the correspondingreceptacle and detecting no code if an object is not present in thecorresponding receptacle; a controller coupled to said sensors forreceiving stored codes detected by said sensors and for determining,based on the received codes, the absence of objects removed from thestorage unit and the presence and location within the storage unit ofobjects present at the storage unit; each of said ID tags comprising aradio frequency identification (RFID) tag, the stored codes of said RFIDtags being transmitted through radio frequency transmission; each ofsaid RFID tags including an antenna for transmission of the stored codewithin the tag and each of said sensors including an antenna forreceiving stored codes transmitted by RFID tags present in acorresponding one of said receptacles.
 2. An object tracking system asclaimed in claim 1 and wherein said antenna of each RFID tag comprises apair of capacitive plates and wherein each of said sensors includes apair of capacitive plates, said capacitive plates of each RFID tagaligning with said capacitive plates of a sensor when the object towhich said RFID tag is attached is disposed in the receptacle associatedwith the sensor, the radio frequency transmission of said ID tag beingcapacitively coupled to said sensor.
 3. An object tracking system asclaimed in claim 2 and wherein said capacitive plates are formed ofconducive foil.
 4. An object tracking system as claimed in claim 2 andwherein said capacitive plates are formed of resistive ink.
 5. An objecttracking system as claimed in claim 2 and wherein said capacitive platesare applied to a surface of said object.
 6. An object tracking system asclaimed in claim 2 and wherein said capacitive plates are embeddedwithin said object.
 7. An object tracking system as claimed in claim 2and wherein said capacitive plates of said sensors are mounted on saidbackplane.
 8. An object tracking system as claimed in claim 7 andwherein the objects are relatively thin cards having a length, a width,and a face, said capacitive plates of each ID tag being substantiallyparallel with the face of its corresponding card and said capacitiveplates of each sensor being formed on an upstanding daughter boardaffixed to said backplane.
 9. An object tracking system as claimed inclaim 8 and wherein said capacitive plates of each ID tag is disposed onthe face of a corresponding card.
 10. An object tracking system asclaimed in claim 8 and wherein said capacitive plates of each ID tag areembedded within a corresponding card.
 11. An object tracking system asclaimed in claim 8 and wherein the capacitive plates of each ID tag areoriented along the width of the corresponding card and wherein thecapacitive plates of said sensors are correspondingly oriented to alignwith the capacitive plates of said ID tags.
 12. An object trackingsystem as claimed in claim 8 and wherein the capacitive plates of eachID tag are oriented along the length of the corresponding card andwherein the capacitive plates of said sensors are correspondinglyoriented to align with the capacitive plates of said ID tags.
 13. Anobject tracking system as claimed in claim 7 and wherein the objects arerelatively thick and have a bottom end that is inserted in a selectedreceptacle when the object is placed in said storage unit, saidcapacitive plates of each ID tag being substantially parallel with thebottom end of the corresponding object and said capacitive plates ofsaid sensors being formed on said backplane.
 14. An object trackingsystem as claimed in claim 13 and wherein the objects are openablecontainers defining an interior space, the bottom ends of the objectshave an interior surface and an exterior surface.
 15. An object trackingsystem as claimed in claim 14 and wherein said capacitive plates of eachID tag are disposed on the interior surface of the bottom end of thecorresponding openable container.
 16. An object tracking system asclaimed in claim 14 and wherein said capacitive plates of each ID tagare embedded within the bottom end of the corresponding openablecontainer.
 17. An object tracking system as claimed in claim 13 andwherein said backplane has a front surface facing said panel and a backsurface facing away from said panel.
 18. An object tracking system asclaimed in claim 17 and wherein said capacitive plates of said sensorsare formed on said front surface of said backplane.
 19. An objecttracking system as claimed in claim 17 and wherein said capacitiveplates of said sensors are formed on said back surface of saidbackplane.
 20. An object tracking system as claimed in claim 17 andwherein said capacitive plates of said sensors are formed by printedcircuit tracings on said backplane.
 21. An object tracking system asclaimed in claim 1 and wherein said antenna of each RFID tag comprisesan inductive loop and wherein each of said sensors includes an inductiveloop, said inductive loops of each RFID tag being supported on saidbackplane and aligning with said inductive loop of a sensor when theobject to which said RFID tag is attached is disposed in the receptacleassociated with the sensor, the radio frequency transmission of saidRFID tag being inductively coupled to said sensor.
 22. An objecttracking system as claimed in claim 21 and wherein the inductive loop ofeach RFID tag is received within the inductive loop of a sensor when theobject to which the RFID tag is attached is inserted within thereceptacle corresponding to said sensor.
 23. An object tracking systemas claimed in claim 21 and wherein the inductive loop of each sensor isreceived within the inductive loop of an RFID tag when the object towhich the RFID tag is attached is inserted within the receptaclecorresponding to said sensor.
 24. An object tracking system as claimedin claim 21 and wherein the inductive loop of each RFID tag isjuxtaposed the inductive loop of a sensor when the object to which theID tag is attached is inserted within the receptacle corresponding tosaid sensor.
 25. In an object tracking system wherein objects to betracked are provided with ID tags storing codes identifying the objectsand the codes of objects present at a location are read by a reader fordetermining the presence or absence of objects at the location, theimprovement comprising a storage unit at the location , said storageunit including a panel formed with openings defining receptacles forreceiving objects to be tracked and a backplane, said reader includingdetectors disposed on said backplane and associated with saidreceptacles, the stored codes being conveyed to the detectors throughradio frequency transmission.
 26. The improvement of claim 25 andwherein the radio frequency transmissions are conveyed to the reader bymeans of an antenna associated with each ID tag and at least one antennaassociated with each of said detectors.
 27. The improvement of claim 26and wherein the antenna associated with each ID tag comprises a pair ofcapacitive plates and the antenna associated with each detectorcomprises a pair of capacitive plates positioned to align with thecapacitive plates of the ID tag of an object disposed in the receptaclecorresponding to the reader.
 28. The improvement of claim 26 and whereinthe antenna associated with each ID tag comprises an inductive loop andthe antenna associated with each detector comprises an inductive looppositioned to align with the inductive loop of the ID tag of an objectdisposed in the receptacle corresponding to the detector.
 29. An objecttracking system for tracking the removal and replacement of objects at alocation, said object tracking system comprising: a storage unit; apanel in said storage unit, said panel being formed with a plurality ofopenings defining receptacles for receiving objects replaced in saidstorage unit; a backplane in said storage unit; a plurality of radiofrequency antennas on said backplane, associated with at least some ofsaid receptacles; a radio frequency identification (RFID) tag on atleast some of the objects to be tracked; and a radio frequency antennacoupled to each RFID tag on objects to be tracked; said radio frequencyantenna on an object aligning with said radio frequency antennaassociated with one of said receptacles when the object is replaced insaid receptacle for radio frequency transmission of signals.
 30. Anobject tracking system as claimed in claim 29 and wherein said radiofrequency antenna on objects and on said backplane comprise capacitiveplates.
 31. An object tracking system as claimed in claim 29 and whereinsaid radio frequency antenna on objects and on said backplane compriseinductive coils.